Spectrometer attachments and phosphorescence decay measurement

ABSTRACT

A spectrometry instrument with exchangeable accessories ( 34, 48, 50, 52 ) providing, for example, different sample presentation facilities. The accessories include a manually operable cam-lock facility ( 54, 68 ) for quick and easy attachment of an accessory to the instrument. The instrument also includes an electrical circuit ( 86-90 ), which is completed by a circuit portion ( 100 ) in an accessory when the accessory is attached to the instrument, for generating a unique identifying voltage ( 94 ) to thereby identify that accessory. This allows for automatic loading in a controlling computer of programs for setting up and running the instrument for measurement regimes using that accessory. The spectrometry instrument is preferably a spectrophotometer used for phosphorescence decay measurements in which sequential phosphorescence emission measurements data from each of a number of excitation cycles applied to a sample are taken and then reassembled into a correct time sequence to define a phosphorescence decay characteristic for the sample, that is, measured data points from a second (and subsequent) excitation cycle are interleaved with those from a first excitation cycle. This significantly reduces the time for establishing a phosphorescence decay characteristic.

TECHNICAL FIELD

[0001] This invention relates to spectrometry instrumentation in generaland in particular examples to fluorescence, phosphorescence andluminescence spectrophotometry.

BACKGROUND

[0002] A fluorescence spectrophotometer usually comprises a flash lightsource, an excitation monochromator or filter, a sample cell containinga sample to be analysed, an emission monochromator or filter, aphotodetector and signal processing electronics. A specific wavelengthof light from the flash source, as selected by the excitationmonochromator or filter, is directed into the sample cell and resultantfluorescence light from the sample enters the emission monochromator orfilter. A specific wavelength of the fluorescence light, as selected bythe emission monochromatolr or filter, is directed onto thephotodetector to produce an electrical signal corresponding to theintensity of the fluorescent light. Such an instrument may be arrangedto make a fluorescence, phosphorescence or luminescence measurement.Fluorescence measurements relate to light which is emitted virtuallyimmediately by a sample upon its exposure to the excitation light,whereas phosphorescence measurements relate to the light emitted fromthe sample a short characteristic time after its exposure to theexcitation light. Luminescence measurements are taken by measuring theemitted light from a sample without exposing the sample to excitationlight. Such measurements are used to characterise substances, withfluorescence measurements in particular having wide application in thebiotechnical field for characterising DNA and other proteins, forexample using fluorofors.

[0003] It is known in spectrometry instruments in general, and inspectrophotometers for fluorescence, phosphorescence and luminescencemeasurements, to provide exchangeable accessories. Generally these mayprovide different sample presentation facilities, for example a liquidsample presentation accessory may be exchanged for one which providesfor presentation of a solid state sample. Different accessories may alsoprovide for temperature control of samples via Peltier, Dewar or othercryostat devices, successive feeding of multiple samples to a readinglocation, or multiple sample carriers such as a well plate and readertherefor.

[0004] In order not to compromise test results, it is important that theexchangeable accessories for a spectrometer be repeatably and accuratelylocatable on the instrument. Prior art arrangements for doing this,which involve screw threaded attachment of one part to another,generally do not facilitate rapid exchange of one accessory for another.

[0005] As described above, the capability to make phosphorescencemeasurements (that is, phosphorescence emission intensity versus time)is included in some fluorescence spectrophotometers. To collectphosphorescence intensity versus time data that results from a shortpulse of excitation light, it is necessary to repetitively measure theemission intensity at a time short enough to adequately define therelationship. The capturing of a data point can be done relativelyquickly via a sample and hold circuit, however the measurement anddigitisation of that data point typically takes a reasonable length oftime. Such data conversion often takes longer than the required intervalbetween successive measured points. By way of example, adequatedefinition of the emission time relationship may require measurement ofthe emission intensity at 1 microsecond intervals yet the digitisationof a single emission datum may take, say, 19.5 microseconds. For thisreason, the prior art technique is to use a sampling approach. In thisarrangement, the excitation light pulse is generated repetitively at aconstant interval. The interval must be long enough for the emissionfrom one pulse to have fallen substantially to zero before the nextpulse is applied. After each excitation pulse a single emissionintensity is measured at a controlled time after the excitation pulse soas to give a single datum of the emission time relationship. For eachsuccessive cycle the time interval between the excitation and capturingof emission intensity is modified so as to build up a complete pictureof the overall emission versus time relationship. In the example givenfor the first cycle the time delay could be 1 microsecond. For thesecond cycle the time delay may be 2 microseconds. For the third thedelay will be 3 microseconds and so on.

[0006] The problem with this approach is that the interval betweenexcitation pulses must be long enough to allow the emission to die awaysubstantially to zero between one pulse and the next. At the same timemany cycles are needed to build up a comprehensive picture of theemission versus time relationship. The overall measurement is thus slow.For example, again referring to the above example of one microsecondintervals between data points, if data covering two milliseconds isdesired then 2000 data points will need to be collected. If the time forthe emission to substantially fall to zero is 10 milliseconds, it willtake 20 seconds to complete the 2000 measurement cycles.

SUMMARY OF THE INVENTION

[0007] According to a first aspect the presen1t invention provides aspectrometry instrument and an exchangeable accessory therefor includinga manually operable mechanism for attaching the exchangeable accessoryto the instrument, the mechanism including a manually rotatable cammingmeans associated with one of the accessory or the instrument, a malemember associated with the other of the accessory or the instrument themale member having a camming surface which is engageable by the cammingmeans, wherein the accessory is positionable on the instrument in apredetermined location and the camming means is manually rotatable toengage the camming surface of the male member and thereby lock theaccessory on the instrument in the predetermined location.

[0008] In spectrometry instruments which have exchangeable accessories,it would be advantageous if the instrument could detect if an accessoryhas been attached and if so, to identify what accessory it is. Theadvantages of this include the instrument's set up and programming foruse with a particular accessory being able to be automaticallyestablished. Also for those accessories that include electricalcomponentry, such as stepper motors, it would be advantageous to detectthe presence of such a component.

[0009] According to a second aspect the present invention provides aspectrometry instrument including an electrical circuit for identifyinganyone of a plurality of exchangeable accessories which are connectableto the instrument, the electrical circuit including a voltage source andmeans for generating an identifying voltage therefrom, wherein eachaccessory includes at least one circuit element such that connection ofan accessory to the instrument alters the identifying voltage to a valuewhich is uniquely dependent upon the accessory which is connected to theinstrument.

[0010] The accessory recognition circuitry may be such that itrecognises the presence of an electric motor of an accessory. In thiscase a voltage divider can be arranged to provide a logic high signal inthe presence of a motor by virtue of the motor winding completing acircuit between the voltage source and the voltage divider. In theabsence of the motor, the circuit is open and a logic low signal isderived from the voltage divider.

[0011] Preferably the spectrometer includes circuitry for identifying anaccessory and further circuitry for determining the presence or absenceof an electric motor in that accessory.

[0012] For a spectrometer with a capacity to have a number of differentaccessories connected thereto at the same time, each connection socketfor each accessory may include accessory recognition circuitry as abovedescribed. In this arrangement, the signal line for the identifyingvoltage from each circuit may be connected to a multiplexer for input toa microprocessor of a computer.

[0013] In a third aspect the present invention provides a method andapparatus for reducing the time for measuring a number of data pointsfor determining a phosphorescence decay characteristic (that is,phosphorescence emission intensity versus time} of a sample.

[0014] According to this third aspect, there is provided a method ofdetermining a phosphorescence decay characteristic of a sample or atleast a portion thereof, including

[0015] i) exposing the sample to a first excitation flash of light,

[0016] ii) measuring the intensity of a decaying phosphorescence lightsignal from the sample caused by the first excitation flash at each of asequence of measurement points which commence a controlled time afterthe first excitation flash and are separated by controlled times,

[0017] iii) exposing the sample to a second excitation flash of lightand

[0018] iv) measuring the decaying phosphorescence light signal from thesample caused by the second excitation flash at each of a sequence ofmeasurement points which commence a controlled time after the secondexcitation flash and are separated by controlled times, wherein the timeinstants to the first and subsequent measurement points from the secondexcitation flash lie between the first and subsequent measurement pointsrespectively from the first excitation flash,

[0019] v) assembling the phosphorescence measurements into time sequenceto produce a phosphorescence decay (characteristic, or a portionthereof, for the sample.

[0020] The assembly of the phosphorescence measurements into timesequence results in the measured data points from the second excitationflash being interleaved with those from the first excitation flash.

[0021] In some cases as the phosphorescence emission from a sampledecays, the time interval between the data points which is required toadequately define the phosphorescence characteristic becomes longer. Theabove described method, in relating to determining possibly only aportion of a phosphorescence decay characteristic, recognises that aftera certain time, the necessary time interval between data points toadequately define the characteristic may be so long as to be able to besequentially measured from the emission caused by one of the excitationflashes and not both. Thus the above described method may be appliedonly for determining an initial or any particular predetermined portionof a decay characteristic.

[0022] The time intervals in step (ii) established by the controlledtimes are greater than the measurement and digitisation time. Theseintervals may be controlled in the sense they are prior determined orcomputed during the data collection process (that is, they are computed“on the fly” from the time for measurement and digitisation of data).The time intervals between measured data points may be uniform or varyfrom one interval to the next. Similarly, the time intervals in step(iv) established by the controlled times may be prior determined ordetermined by computation during the data collection process.

[0023] The method may be extended wherein further excitation flashes areinitiated and further phosphorescence emission intensity measurementstaken which result from each such further excitation flash, the furtherphosphorescence measurements for each such further excitation flashbeing taken at controlled times (ie., prior determined or computed timesas above described) such that each such further phosphorescencemeasurement can be interleaved between phosphorescence measurementsresulting from earlier excitation flashes. That is, steps (iii) and {iv)may be repeated as often as necessary until all required measured pointsare obtained.

[0024] According to this third aspect of the invention there is alsoprovided apparatus for performing the above described method. Thisapparatus comprises a spectrophotometer and means for controlling thespectrophotometer, said means for controlling being such as to acquiresequential phosphorescence emission measurements data from each of anumber of excitation cycles applied to a sample in the spectrophotometerand to assemble that data into a correct time sequence to define aphosphorescence decay characteristic, or a portion thereof, for thesample.

[0025] The means for controlling the spectrophotometer may be a suitablyprogrammed computer or a dedicated device or circuitry.

[0026] Preferably this apparatus includes a manually operable mechanismfor attaching an exchangeable accessory as described herein above. Theapparatus also preferably includes an accessory recognition circuit asalso described hereinabove.

[0027] The following detailed description with reference to drawings isprovided to give a better understanding of the invention and to show howit may be carried into effect in all its aspects. This description andthe drawings are given by way of non-limiting example only and are notto be interpreted as limiting the generality of the precedingdescription.

BRIEF DESCRIPTION OF DRAWINGS

[0028]FIG. 1 diagrammatically illustrates a spectrophotometer formeasuring fluorescence or phosphorescence from a sample;

[0029] FIGS. 2 to 4 illustrate a manually operable mechanism forattaching an accessory to a spectrophotometer;

[0030]FIGS. 5 and 6 illustrate accessory recognition circuitry for usein a spectrophotometer;

[0031]FIGS. 7A and 78 illustrate data acquisition circuits; and

[0032]FIG. 8 diagrammatically illustrates a phosphorescence measurementregime.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] A fluorescence spectrophotometer, as diagrammatically illustratedin FIG. 1, includes a Xenon flash light source 20, the light 22 fromwhich is directed into an excitation monochromator 24. Light 26 of aselected wavelength which exits monochromator 24 passes through a beamsplitter 28 to derive a reference beam 30 the intensity of which ismeasured by a detector 32. Excitation light 26 continues from beamsplitter 28 and irradiates a sample in sample holder 34. Thefluorescence (or phosphorescence) light 36 emitted by the sampletraverses an emission monochromator 38, the light of a selectedwavelength 40 of which the intensity is measured by detector 42. Theemission monochromator is arranged to be off the axis of the excitationmonochromator 24. Drivers 44 and 46 for each of the monochromators 24,38 respectively, allow for wavelength, filter and slit width selection.

[0034] Operation of the spectrophotometer is controlled by a computer orother means (not shown in FIG. 1) such that slit: widths and filters areselectable according to wavelength and controlled by stepper motorsallowing either manual or automatic selection. Slit selector is usercontrolled. The computer or other control means also controls the dataacquisition electronics (to be described below) and the manipulation ofthe data, notably for phosphorescence measurements, also to be describedbelow.

[0035] The detectors 32 and 42 are photomultiplier tubes. If the lighttight sample compartment door of the instrument is opened allowingincident light to reach the photomultiplier tubes 32 and 42, thefirmware recognises this overrange condition and causes a filter to bemoved to block the entry of the incident light into the photomultipliertubes and/or reduce the EHT power supply. Another protection feature isthat monochromators 24 and 38 include safety interlocks for preventing azero order setting for slit widths greater than 5 nm. The instrumentincludes exchangeable accessories schematically represented at 48, 50and 52. Such accessories generally provide for different samples andsample presentation regimes and are thus exchangeable in relation to thesample holder 34. The instrument may simultaneously have a number, forexample up to four, different accessories connected thereto. Allaccessories require mechanical attachment to a sample compartment of theinstrument and in one aspect this invention provides a quick, simple andreliable attachment mechanism for this. The sample compartment of aspectrometer is an accessible space within the spectrometer wherein asample is conveniently placed for the purpose of making spectrometricmeasurements. A sample compartment is typically provided with means tohold a sample in a precisely defined position with respect to the pathsof light beams in the spectrometer, and is provided with apertures forthe passage of said light beams. In another aspect the inventionprovides electrical means for detecting the presence or absence of anaccessory, and if an accessory is attached and plugged in, identifyingthat accessory so that appropriate software programmes for measurementregimes using that accessory may be automatically loaded. This savesuser time in that the user does not then have to search for the relevantprogrammes.

[0036] With reference to FIG. 24, the mechanical attachment mechanismfor an accessory such as 48 comprises a manually rotatable camming means54 associated with the accessory 48. FIG. 2 shows an underneath view ofthe base 56 of an accessory 48 on which is mounted for rotation a shaft58 for manually rotating the camming means 54 via a handle 60 (a platewhich is attachable to the base 56 for covering the shaft 58 has beenomitted from FIGS. 2 and 3). FIG. 3 shows a section of FIG. 2 on lineIII-III.

[0037] Ideally the camming means is rotated through less than 360° toattach the accessory and more ideally its rotation is about 180°,Preferably the camming means has a female form for receiving the malemember, for example it may be spherical or cylindrical with a recessformed therein having a curved camming surface which interacts with thecamming surface of the male member. The camming means is preferablylocated substantially centrally of a base of the accessory and isoperable via a shaft which extends to a peripheral surface of theaccessory for manual operation. Preferably the shaft includes a handleor knob for facilitating its manual rotation.

[0038] Preferably the male member is associated with and is biased in adirection towards the instrument such that, as the camming means and themale member become engaged, the male member is moved in a direction awayfrom the instrument against the bias. This ensures that when the cammingmeans and the male member are fully engaged to lock the accessory ontothe instrument, a positive holding force is maintained on the accessory.

[0039] Alternatively the camming means may be associated with theinstrument and the male member with the accessory.

[0040] Preferably the accessory and the instrument include a number ofcomplementary projections such as pins on and recesses in their facingsurfaces for establishing the predetermined location for the accessoryon the I instrument. Thus, as the camming means is rotated to engage themale member and draw the accessory towards the instrument, theprojections, which are preferably on the accessory, locate incomplementary recesses which are preferably in the instrument, to ensurethe correct location of the accessory on the instrument.

[0041] It will be appreciated that embodiments of the invention asdescribed above and to be described in more detail below provide aneasily manually operable attachment mechanism which allows quickattachment and release of an accessory from a spectrometry instrumentwhich is preferably a spectrophotometer. This quick attachment andrelease advantage of the invention is derived from the mechanism's useof a single attachment point and the actual attachment being achieved byan approximate half turn of the camming means via a prominentlyaccessible handle, knob or the like.

[0042] The camming means 54 comprises a cylinder 62 within which arecess 64 is formed which provides a curved camming surface 66.

[0043] A male member 68 (see FIG. 3) is mounted in the base 70 of thesample compartment of the instrument and includes an outer sphericalform 72 which is engageable by the camming means 54, specifically itscamming surface 66, whereby rotation of the camming means 54 via handle60 causes its surface 66 to interact with spherical surface 72 of malemember 68 to draw the accessory base 56 into facing contact withinstrument blase 70 and lock the accessory on the instrument in apredetermined location. The predetermined location is determined by therelative locations of the camming means 54 and the male member 68 and bycomplementary location means on an accessory and the instrument. Thesecomplementary location means may comprise protrusions 74 on theaccessory base 56 (only one of which is shown in FIGS. 2 and 3) whichare locatable in recesses 76 in the instrument base 70. A convenient andpreferred mechanism for spatially locating the accessory in the samplecompartment is to use a kinetic mount. This consists of three protrudingpegs on either the instrument or the accessory .The first peg engages ina hole in the mating surface and thereby accurately locates one point ofthe accessory to the instrument. Height control may be achieved eitherby the peg resting on the bottom of a blind hole or a shoulder on thepeg resting on the top of the hole. The second peg locates in a slot inthe mating surface whose centre line passes through the centre of thepreviously mentioned hole. It uses similar means of height control asfor the first peg. This controls angular position of the accessory withreference to the first location point. The third peg rests on a plate onthe mating surface.

[0044] The spherical form 72 of the male member 68 is at the end of astem 78 mounted in a sleeve 80 and biased inwardly relative thereto by aspring 82. The sleeve 80 is screw-threaded at a lower 01″ inner end 84for attachment in an aperture 86 in the base. Thus as the camnning means54 engages the male member 68 and is rotated relative thereto the spring82 acts to bias the spherical form 72 downwardly towards the base 70 ofthe instrument. This ensures that when the camming means 54 and the malemember 68 (specifically the surfaces 66 and 72) are fully engaged tolock the accessory 48 onto the instrument, a positive holding forcemaintained on the accessory.

[0045] The accessory 48 is releasable simply by reversely manuallyrotating the handle 60 to release the spherical form 72 from the cammingsurface 66 and lifting the accessory away.

[0046] The spectrophotometer includes a number of sockets, for examplefour, .in its sample compartment for receiving plugs on the accessories,that is, each accessory has a plug which is receivable in anyone of thefour sockets. An accessory recognition circuit in the spectrophotometerincludes a voltage source 86 (see FIG. 5) the negative side of which isconnected to ground and the positive to a means for generating anidentifying voltage in the form of a voltage divider comprisingresistors 88 and 90. The series connection of the source 86 andresistors 88 and 90 is connected to a dedicated pin 92 of a socket inthe sample compartment. A signal line 94 is connected between theresistors 88 and 90 and a multiplexer 96, and then to an analog todigital converter 98 and a microprocessor (not shown) for reading thedata and controlling operations. An identifying voltage for an accessoryis read via signal line 94. If there is no accessory present, thiscircuit is open and the voltage of source 86 is read on line 94.

[0047] Preferably the means for generating an identifying voltage is avoltage divider and this together with the voltage source provide anopen electrical circuit such that in the absence of an accessory theidentifying voltage floats to the voltage of the voltage source, therebyidentifying the absence of an accessory. Preferably each accessoryprovides a circuit element for completing the electrical circuit of thespectrophotometer when connected thereto. The circuit element of eachaccessory is different such that when it completes the circuit includingthe voltage source and the voltage divider of the spectrometer, itcauses the identifying voltage to change to a value which is unique forthat accessory. The identifying voltage which is generated is read by amicroprocessor which identifies the particular accessory, or absence ofan accessory I connected to the spectrometer, which is preferably aspectrophotometer.

[0048] The circuit element of an accessory, may simply provide a linkwhich connects to ground, or a particular voltage of the instrument, eg.+5V, +12V, +15V or −15V, depending on the accessory. This arrangementcan be used for accessories which do not include their own electronics.For accessories which do include their own electronics and thus acircuit board and a plurality of circuit elements, a resistor maybe-included which connects between the circuit of the instrument and aconnection to ground. +5V, +12V, +15V or −15V. It will be evident that anumber of circuit combinations are possible to provide for a number ofdifferent accessories. For example, a circuit element of an accessory inthe form of a link that connects to ground, +5V, +12V, +15V or −15Vgives 5 combinations. That is, it gives the possibility of generatingfive unique voltages and thereby the identification of five differentaccessories.

[0049] Connection of an accessory to the socket may provide a circuitelement in the form of a link (not shown) to ground, or to an analogvoltage, say +5 volts, +12 volts, +15 volts or −15 volts on other pirlsof the socket, depending on the particular accessory. When such a linkis made, the voltage appearing on line 94 will alter to a value which isuniquely dependent upon the particular link established by thataccessory. Thus the vol1 age signal on line 94 can be used by themicroprocessor to identify a particular accessory. Such a link forcompleting the circuit of the instrument is suitable for accessorieswhich do not include their own circuitry. Furthermore the possibility ofthe link connecting to ground, +5 volts, +12 volts, +15 volts or −1Eivolts provides five combinations, that is, it allows the identificationof five different accessories.

[0050] The multiplexer includes four signal inputs, one from each of acircuit such as is illustrated associated with each of 1the fouraccessory sockets.

[0051] Alternatively where an accessory does include its own circuitry,a resistor 100 may be added which is connectable, via the plugging in ofan accessory to one of the instrument sockets, to ground or ˜3 supplyvoltage such as +5 volts, +12 volts, +15 volts or −15 volts at pin 102.This will also alter the voltage on signal line 94 to a unique value forthe particular accessory concerned. This allows more combinations forthe identifying voltages 94 than the previous arrangement of using onlya link. Alternatively the resistor 100 may be connected to or replacedby a programmable voltage source to allow for re-configurableaccessories.

[0052] For an accessory with a stepper motor, the recognition circuitrymay comprise a pull-up resistor 104 (see FIG. 6) connected between avoltage source 106 (eg. 12V) of the instrument and a pin 108 of theaccessory socket. A voltage divider comprising resistors 110, 112 isconnected between another pin 114 of the socket and ground. A signalline 116 is connected between the voltage divider resistors 110, 112.Motor drivers 118, 120 are connected to the pins 108, 114. FIG. 6 showsa motor of an accessory having a winding 122 connected across the pins108, 114. On power up the motor drivers 118, 120 are disabled and pullup resistor 104 and voltage divider 110-112 generate a “motor present”signal, that is, if there is a motor winding connected across pins 108,114 a current flows through the voltage divider 110-112 which generatesa logic high signal (indicating “motor present”) which is read by themicroprocessor (not shown) to which signal line 116 leads. If a motor isnot present, a logic low signal on line 116 is read by themicroprocessor.

[0053] The plug of an accessory may be arranged on the accessory suchthat it automatically mates with a socket of the instrument as theaccessory is attached thereon via a mechanical attachment mechanism asdescribed hereinabove. Thus the one action of attaching an accessory mayautomatically establish its electrical connection to the instrument andcompletion of the recognition circuitry and the possible consequentialautomatic loading of programmes.

[0054] A data acquisition circuit of an instrument as in FIG. 1 isdiagrammatically illustrated in FIG. 7A. This circuit comprises anamplification stage 124 connected to a detector 42 as in FIG. 1. Theoutput of the amplification stage 124 is connected to a sample and holdcircuit 126, the output of which is i connected to an analog to digitalconverter 128 which supplies the data to a microprocessor of a computer130. The instrument is computer controlled and this is represented byline 132 (alternatively the instrument may be controlled by a dedicateddevice or circuitry). Multiple channel data acquisition circuits may beprovided, or as illustrated, separate sample and hold circuits 134, 136etc, each followed by an analog to digital converter {not shown) may beconnected between the amplification stage 124 and the computer 130. FIG.78 illustrates a modification of the FIG. 7A circuit, namely theaddition of control circuitry 138 which receives a signal on line 140from an AID converter 128 indicating that a conversion is complete andsending a signal on line 142 to a sample and hold circuit 126, 134, 136to start another conversion. That is, the additional circuitry 138-142determines the measurement time dynamically, typically initiating thenext conversion whenever one of the conversion circuits becomes idle.

[0055] Use of a fluorescence spectrophotometer as in FIG. 1 having adata acquisition circuit as in FIG. 7 and which may have either or bothof the accessory attachment and accessory recognition features describedhereinabove, for making phosphorescence measurements will now bedescribed to exemplify the third aspect of the invention.

[0056] A problem with a data acquisition circuit such as that of FIG. 7Aor 78 is that the gate time for the digitisation and reading of a sampledata point from the sample and hold circuit 126 by the analog to digitalconverter 128 and microprocessor 130 usually exceeds the time space inbetween the data points which is necessary to adequately define thephosphorescence decay characteristic of the sample. That is, theelectronics is not fast enough to convert all of the necessary data,hence a relatively high number of flash and read cycles have to beperformed, with only one data point being collected for each cycle.

[0057] The controlled times between the phosphorescence emissionmeasurement points for a particular excitation flash may be equal, withthe time to the first measurement point resulting from the secondexcitation flash being different to and preferably longer than the timeto the first measurement point resulting from the first excitationflash. Continuing with this sequence, the time to the first measurementpoint resulting from a third excitation flash will be greater than thetime to the first measurement point resulting from the second excitationflash, and likewise for any subsequent excitation flashes.

[0058] Effectively the time to the first phosphorescence measurementpoints resulting from the first and subsequent excitation flashes arerespectively offset such that the first measurement point resulting fromthe second excitation flash follows the first measurement pointresulting from the first excitation flash, and the first measurementpoint resulting from a ti″1 ird excitation flash follows the firstmeasurement point resulting from the second excitation flash, andlikewise for any subsequent excitation flashes.

[0059] The controlled time periods may be such that the interleaved datapoints are separated by equal time intervals. Alternatively thecontrolled time periods may be such that the interleaved data points areseparated by unequal time periods. That is, this third aspect of theimention encompasses an operator being able to decide the particulartime intervals that will exist between successive interleaved datapoints which define the phosphorescence decay characteristic. Theseparticular time intervals may be equal or unequal and varied, as theoperator determines.

[0060]FIG. 8 illustrates a phosphorescence decay characteristic 200(intensity vs. time) for a sample for which it is desiredthat,measurement data at points 202-215 be collected to define thecharacteristic. Sample integration periods for the data points 202-216are shown at time-lines (b), (c), (d) and (e). The time intervals shownalong time-line (a) represent the time for the data of a measurementpoint to be transferred to the computer. This time is greater than thespacing between the data points 202-21), thus the computer cannotcollect the data of all the desired measurement points in one pass.

[0061] According to the invention, several decay scans are performed andthe data from each are interleaved in a correct time sequence to derivethe phosphorescence decay characteristic. The measurement regime isunder control of computer 130 which keeps track of all thedelay/emission data points required to define the phosphorescence decaycharacteristic. Following an excitation flash, the data acquisitionelectronics 42-124-126-128-130 completes collection of the first datum202 as represrented by time interval at (a), the computer notes the timefrom the excitation pulse, looks for the next unmeasured point 206 afterthat time and triggers the data acquisition electronics to collect thatpoint as well, and so on for the illustrated datums 210 and 214. Thusseveral data points are measured on the one cycle as shown at (b). Thenext excitation pulse is then triggered, and under the control of thecomputer, the data points 203, 207, 211,215 are collected, as shown at(c) and so on for as many cycles as are required to collect all thedesired data points, see (d) and (e).

[0062] The computer then assembles all the measured data points into thecorrect overall time sequence to create the complete phosphorescencecharacteristic. For example, if measurement at 1 microsecond intervalsis required to define the phosphorescence ch.3racteristic and theacquisition of each measurement data point takes 19.5 microseconds, onthe first cycle the emission at 1 microsecond is measured. This data istransferred to the computer at 20.5 microseconds. The next data pointrequired is at 21 microseconds so the computer triggers the electronicsto collect this point. The second point is transferred to the computerat time 40.5 microseconds. The next data point required is at 41microseconds and so the computer triggers the electronics to collectthis point, and so on. On the second cycle, the computer collects datafor times 2 microseconds, 22 microseconds, 42 microseconds etc. In thisexample, for data covering 2 milliseconds, all points can be collectedin 20 cycles instead of 2000 cycles for the prior art approach, reducingthe overall measurement time from 20 seconds to 200 milliseconds.

[0063] The time intervals between the data points may vary or be fixedand is not critical to the invention, which is characterised by thecollection of more than one data point from each cycle and thereassembly of those data points into the correct time sequence withinthe associated computer system.

[0064] This third aspect of the invention offers several advantages. Thefirst is the time saving leading to increased productivity. Some sampleshave the characteristic of changing their properties with time or withthe amount of excitation light received. The invention reduces both themeasurement and the total integrated amount of excitation light imposedon the sample thereby minimising this source of measurement uncertainty.

[0065] In order to obtain good time precision for short duration 15phosphorescence events the duration of the excitation pulse needs to beshort while at the same time delivering a high total I light flux to thesample. A xenon flash lamp 20 meets these requirements of short durationand high intensity and is thus a desirable source for such applications.It has however the disadvantage that the light output per flash isvariable. Since the emission signal is proportional to the excitationsignal such variation must be allowed for if accurate results are to beobtained. To this end, in the implementation of the phosphorescencemeasurement method, the excitation flux for each pulse is measured atthe start of each cycle and used to normalise the emission measurementscollected during that cycle. That is, as is known, a dark signal ismeasured for the sample for each cycle, and a dark signal and referencesignal for the reference beam 30 which are used to normalise theresults.

[0066] A further variant on this third aspect is to use two or moreindependent sets of measurement and digitisation electronics operatingfrom the same signal source and all capable of transmitting thedigitised value to the processor. In this case the processor initiates afirst excitation flash of light and as each measurement time instant isreached it triggers the next available set of measurement anddigitisation electronics to acquire the value. This variant has theadvantage of achieving still shorter data collection times but at theexpense of greater electronic cost and complexity. Thus two or moreindependent sets of digitisation electronics may be used in conjunctionwith multiple flashes to give still greater speeds.

[0067] Preferably a reference intensity measurement is taken of everyexcitation flash of light, and the phosphorescence emission intensitymeasurements derived from that flash are ratioed with the reference tocompensate for differences in intensity which may occur between flashes.As is known such compensation may include dark signal measurements beingtaken immediately before an excitation flash and subtracted from themeasured excitation and emission intensities for the ratioing.

[0068] The invention in each of its aspects as described herein issusceptible to variations, modifications and/or additions other thanthose specifically described and it is to be understood that theinvention includes all such variations, modifications and/or additionswhich fall within the scope of the following claims.

1. A spectrometry instrument and an exchangeable accessory thereforincluding a manually operable mechanism for attaching the exchangeableaccessory to the instrument, the mechanism including a manuallyrotatable camming means associated with one of the accessory or theinstrument, a male member associated with the other of the accessory orthe instrument, the male member having a camming surface which isengageable by the camming means, wherein the accessory is positionableon the instrument in a predetermined location and the camming means ismanually rotatable to engage the camming surface of the male member andthereby lock the accessory on the instrument in the predeterminedlocation.
 2. A spectrometry instrument and an exchangeable accessorytherefor as claimed in claim 1 wherein the camming means includes a bodyhaving a recess formed therein, the recess having a curved cammingsurface which, interacts with the camming surface of the male member. 3.A spectrometry instrument and an exchangeable accessory therefor asclaimed in claim 2 wherein the camming surface of the male member issubstantially spherical, and the recess of the camming means has asubstantially complementary shape.
 4. A spectrometry instrument and anexchangeable accessory therefor as claimed in anyone of claims 1 to 3wherein the male member is biased in a direction towards the instrumentor accessory with which it is associated, whereby engagement of thecamming means with the camming surface of the male member moves the malemember against the bias.
 5. A spectrometry instrument and anexchangeable accessory therefor as claimed in anyone of claims 1 to 4wherein the camming means and male member are substantially centrallylocated of facing surfaces of the instrument and the accessory.
 6. Aspectrometry instrument and an e)(changeable accessory therefor asclaimed in anyone of claims 1 to 5 wherein facing surfaces of theinstrument and the accessory include projections and complementaryrecesses for establishing said predetermined location.
 7. A spectrometryinstrument and an exchangeable accessory therefor as claimed in claim 5wherein the camming means includes a shaft which extends to a peripheralsurface of the instrument or accessory with which the camming means isassociated, and a handle or knob 011 the shaft adjacent said peripheralsurface for facilitating manual operation of the camming means.
 8. Aspectrometry instrument and an exchangeable accessory therefor asclaimed in anyone of claims 1 to 7 wherein the camming means isassociated with the accessory and the male member is associated with theinstrument.
 9. A spectrometry instrument including an electrical circuitfor identifying anyone of a plurality of exchangeable accessories whichare connectable to the instrument, the electrical circuit including avoltage source and means for generating an identifying voltagetherefrom, wherein each accessory includes at least one circuit elementsuch that connection of an accessory to the instrument alters theidentifying voltage to a value which is uniquely dependent upon theaccessory which is connected to the instrument.
 10. A spectrometryinstrument as claimed in claim 9 wherein the means for generating anidentifying voltage from the voltage source is a voltage divider.
 11. Aspectrometer as claimed in claim SI or claim 10 wherein the voltagesource and means for generating an identifying voltage provide an openelectrical circuit such that in the absence of an accessory .theidentifying voltage becomes the voltage of the voltage source therebyidentifying the absence of an accessory.
 12. A spectrometer as claimedin claim 11 wherein the at least one circuit element of an accessorycompletes said open electrical circuit.
 13. A spectrometer as claimed inclaim 12 wherein the at least one circuit element of an accessory is acircuit link which connects the electrical circuit of the instrument tothe instrument ground or a predetermined one of a plurality of voltagesof the instrument, depending on the accessory.
 14. A spectrometer asclaimed in claim 11 wherein the accessory includes a plurality ofcircuit elements which complete said open electrical circuit.
 15. Aspectrometer as claimed in claim 9 wherein the at least one circuitelement is a winding of an electrical motor of an accessory, whereby theidentifying voltage is altered to a value which uniquely identifies thepresence of the electrical motor.
 16. A spectrometer as claimed in claim9 wherein the electrical circuit of the II′ instrument additionallyprovides for recognition of the presence of an electrical motor in anaccessory.
 17. A spectrometer as claimed in claim 16 wherein the windingof the motor completes an electrical circuit of the instrument whichincludes a voltage divider whereby a logic high signal is generated bythe presence of the winding and a logic low signal in the absence of thewinding.
 18. A spectrometer as claimed in anyone of claims 9 to 17including a computer having a microprocessor for reading the identifyingvoltage and which thereby identifies the accessory connected to theinstrument.
 19. A spectrometer as claimed in claim 18 wherein thecomputer is programmed to automatically load programmed for operatingthe instrument in measurement regimes involving the accessory which isconnected to the instrument.
 20. A method of determining aphosphorl3SCence decay characteristic of a sample, or at least a portionthereof, including i) exposing the sample to a first excitation flash oflight, ii) measuring the intensity of a decaying phosphorescence lightsignal from the sample caused by the first excita1tion flash at each ofa sequence of measurement points which commence a controlled time afterthe first excitation flash and are separated by controlled times, iii)exposing the sample to a second excitation flash of light and iv) iv)measuring the decaying phosphorescence light signal from the samplecaused by the second excitation flash at each of a sequence ofmeasurement points which commence a controlled time after the secondexcitation flash and are separated by controlled times, wherein the timeinstants to the first and subsequent measurement points from the secondexcitation flash lie between the first and subsequent measurement pointsrespectively from the first excitation flash, v) assembling thephosphorescence measurements into time sequence to produce aphosphorescence decay characteristic, or a portion thereof, for thesample.
 21. A method as claimed in claim 20 including repeating steps(iii) and (iv) in respect of further excitation flashes of light,respectively, wherein the further phosphorescence measurements for eachsuch further excitation flash are taken at controlled times-such that fnstep (v) each said further phosphorescence measurement is interleavedbetween phosphorescence measurements resulting from earlier excitationflashes.
 22. A method as claimed in claim 20 or 21 wherein thecontrolled times are such that the time intervals between the assembledphosphorescence measurements of step (v) are equal.
 23. A method asclaimed in claim 20 or 21 wherein the controlled times are such that thetime intervals between the assembled phosphorescence measurements ofstep (v) vary from one internal to the next.
 24. A method as claimed inclaim 20 or claim 21 wherein the controlled times separating the firstand subsequent measurement points of the decaying phosphorescence lightsignal from, respectively, the first and second and any subsequentexcitation flashes are determined prior to commencement of the method.25. A method as claimed in claim 20 or claim 21 wherein the controlledtimes I separating the first and subsequent measurement points of thedecaying phosphorescence light signal from, respectively, the first andsecond and any subsequent excitation flashes are determined during themethod.
 26. A method as claimed in claim 25 wherein the controlled timebetween successive measurement points of the decaying phosphorescencesignal caused by an excitation flash is determined to be greater than atime for measurement and digitization of data from a previousmeasurement point.
 27. Apparatus for determining a phosphorescence decaycharacteristic of a sample or at least a portion thereof comprising aspectrophotometer and a means for controlling the spectrophotometer,wherein the means for controlling is arranged to acquire sequentialphosphorescence emission measurements data from each of a number ofexcitation cycles applied to a sample in the spectrophotometer and toassemble that data into a correct time sequence to define aphosphorescence decay characteristic, or portion thereof, for thesample.
 28. Apparatus as claimed in claim 27 wherein thespectrophotometer includes a data acquisition circuit for the sequentialphosphorescence emission measurements data, the data acquisition circuitincluding a sample and hold stage followed by an analog to digitalconversion stage from which the data is acquired by the means forcontrolling, wherein the means for controlling is arranged forsequential phosphorescence emission measurements from each excitationcycle to be taken at time intervals which are longer than the timerequired for conversion of measurement data to occur in the analog todigital conversion stage and be acquired by the means for controllingthe spectrophotometer .
 29. Apparatus as claimed in claim 28 wherein themeans for controlling is arranged for a first measurement ofphosphorescence emission from the first and subsequent excitation cyclesto be respectively offset in time such that the first measurementresulting from a second excitation cycle follows the first measurementresulting from a first excitation cycle, and the first measurementresulting from a third excitation cycle follows the first measurementresulting from the second excitation cycle, and likewise for subsequentexcitation cycles, whereby the assembly of the measurements data into acorrect time sequence results in the measurements from the second andsubsequent excitation cycles being interleaved with the measurementsfrom the first excitation cycle.
 30. Apparatus as claimed in claim 27,28 or 29 wherein the means for controlling the spectrophotometer is aprogrammable computer.
 31. Apparatus as claimed in anyone of claims 27to 30 wherein the pectrophotometer includes an exchangeable accessory,the apparatus including a manually operable mechanism for attaching theexchangeable accessory to the instrument, the mechanism including amanually rotatable camming means associated with one of the accessory orthe instrument, a male member associated with the other of the accessoryor the instrument, the male member having a camming surface which isengageable by the camming means, wherein the accessory is positionableon the instrument in a predetermined location and the camming means ismanually rotatable to engage the camming surface of the male member andthereby lock the accessory on the instrument in the predeterminedlocation.
 32. Apparatus as claimed in anyone of claims 27 to 30 whereinthe pectrophotometer includes an electrical circuit for identifyinganyone of a plurality of exchangeable accessories which are connectableto the instrument, the electrical circuit including a voltage source andmeans for generating an identifying voltage therefrom, wherein eachaccessory includes at least one circuit element such that connection ofan accessory to the instrument alters the identifying voltage to a valuewhich is uniquely dependent upon the accessory which is connected to theinstrument.
 33. Apparatus as claimed in claim 31 wherein thespectrophotometer further includes an electrical circuit for identifyinganyone of a plurality of exchangeable accessories which are connectableto the instrument, the electrical circuit including a voltage source andmeans for generating an identifying voltage therefrom, wherein eachaccessory includes at least one circuit element such that connection ofan accessory to the instrument alters the identifying voltage to a valuewhich is uniquely dependent upon the accessory which is connected to theinstrument.